Calcium ions play a critical role in signaling in a wide variety of tissues, including muscle, immune cells, neurons, the liver and oocytes. They can enter the cytoplasm from the extracellular environment or from intracellular stores and control the activity of numerous enzymes, other signaling molecules, transcription factors, and cytoskeletal components. Much is known about regulation of calcium fluxes, the channels and pumps that transport calcium between different compartments, cytosolic calcium buffers and sensors and how these produce distinct spatiotemporal calcium signals in different circumstances. This book covers these relatively well established aspects of the field, together with newer work implicating calcium in the regulation of apoptosis during normal physiology and necrotic cell death in pathological conditions such as stroke and ischemia.